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Microwave Conductivity (microwave + conductivity)

Distribution by Scientific Domains

Physics and Astronomy	50%

Selected Abstracts

The Effect of Nanoparticle Shape on the Photocarrier Dynamics and Photovoltaic Device Performance of Poly(3-hexylthiophene):CdSe Nanoparticle Bulk Heterojunction Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 16 2010
Smita Dayal
Abstract The charge separation and transport dynamics in CdSe nanoparticle:poly(3-hexylthiophene) (P3HT) blends are reported as a function of the shape of the CdSe-nanoparticle electron acceptor (dot, rod, and tetrapod). For optimization of organic photovoltaic device performance it is crucial to understand the role of various nanostructures in the generation and transport of charge carriers. The sample processing conditions are carefully controlled to eliminate any processing-related effects on the carrier generation and on device performance with the aim of keeping the conjugated polymer phase constant and only varying the shape of the inorganic nanoparticle acceptor phase. The electrodeless, flash photolysis time-resolved microwave conductivity (FP-TRMC) technique is used and the results are compared to the efficiency of photovoltaic devices that incorporate the same active layer. It is observed that in nanorods and tetrapods blended with P3HT, the high aspect ratios provide a pathway for the electrons to move away from the dissociation site even in the absence of an applied electric field, resulting in enhanced carrier lifetimes that correlate to increased efficiencies in devices. The processing conditions that yield optimum performance in high aspect ratio CdSe nanoparticles blended with P3HT result in poorly performing quantum dot CdSe:P3HT devices, indicating that the latter devices are inherently limited by the absence of the dimensionality that allows for efficient, prolonged charge separation at the polymer:CdSe interface. [source]

Temperature-Resolved Local and Macroscopic Charge Carrier Transport in Thin P3HT Layers,

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010
Patrick Pingel
Abstract Previous investigations of the field-effect mobility in poly(3-hexylthiophene) (P3HT) layers revealed a strong dependence on molecular weight (MW), which was shown to be closely related to layer morphology. Here, charge carrier mobilities of two P3HT MW fractions (medium-MW: Mn,=,7,200 g mol,1; high-MW: Mn,=,27,000 g mol,1) are probed as a function of temperature at a local and a macroscopic length scale, using pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) and organic field-effect transistor measurements, respectively. In contrast to the macroscopic transport properties, the local intra-grain mobility depends only weakly on MW (being in the order of 10,2 cm2 V,1 s,1) and being thermally activated below the melting temperature for both fractions. The striking differences of charge transport at both length scales are related to the heterogeneity of the layer morphology. The quantitative analysis of temperature-dependent UV/Vis absorption spectra according to a model of F. C. Spano reveals that a substantial amount of disordered material is present in these P3HT layers. Moreover, the analysis predicts that aggregates in medium-MW P3HT undergo a "pre-melting" significantly below the actual melting temperature. The results suggest that macroscopic charge transport in samples of short-chain P3HT is strongly inhibited by the presence of disordered domains, while in high-MW P3HT the low-mobility disordered zones are bridged via inter-crystalline molecular connections. [source]

Dynamics of photogenerated carriers in porous silicon probed by microwave absorption

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2007
H. E. PorteanuArticle first published online: 27 APR 200
Abstract We report on dynamics of photogenerated carriers in porous silicon using contactless investigation tools. A comparison of two theoretical models: the simple point charge description versus degenerate gas model is presented. The temperature dependence reveals the dominant role of surface states below 70 K. Light intensity dependences evidence Auger processes. The optical and chemical properties can be indirectly improved using the microwave conductivity by studying the surface states of porous materials. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Influence of electronic correlations on the frequency-dependent hopping transport in Si:P

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008
Elvira Ritz
Abstract At low energy scales charge transport in the insulating Si:P is dominated by activated hopping between the localized donor electron states. Thus, theoretical models for a disordered system with electron-electron interaction are appropriate to interpret the electric conductivity spectra. With a newly developed technique we have measured the complex broadband microwave conductivity of Si:P from 100 MHz to 5 GHz in a broad range of phosphorus concentration n /nc from 0.56 to 0.95 relative to the critical value nc = 3:5 × 1018 cm,3 corresponding to the metal-insulator transition driven by doping. At our base temperature of T = 1.1 K the samples are in the zero-phonon regime where they show a super-linear frequency dependence of the conductivity indicating the influence of the Coulomb gap in the density of the impurity states. At higher doping n , nc, an abrupt drop in the conductivity power law ,1(,) , ,, is observed. The dielectric function ,1 increases upon doping following a power law in (1 , n /nc). Dynamic response at elevated temperatures has also been investigated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]